Light

ABSTRACT

A light is disclosed which may be an aircraft light, comprising a base  2  for mounting the light, a chassis  8  upstanding from the base, a circuit board  10  mounted upon an outer face of the chassis and at least one solid state emitter—and more preferably an aray of LEDs  24, 26— mounted upon the circuit board. The invention provides a light which is constructionally convenient but can provide a clean beam pattern.

[0001] The present invention is concerned with solid state lights.

[0002] Conventional incandescent lights are being increasingly replacedby solid state lights, notably light emitting diodes (LEDs) which havesubstantially increased reliability and lower maintenance costs. Thishas traditionally been at the expense of brightness and coloursrestricted to red, green and yellow but the latest technologies nowenable LEDs to compete in many more applications where incandescentlight bulbs with coloured filters are conventionally used.

[0003] Nonetheless using LEDs to replace incandescent bulbs involvescareful optical design, not least because the light emitted from thesolid state chip is directional and to enable it to leave the chip(inside which it is generated) without reflection at the chip's insidesurface, the chip has to be covered with a transparent high refractiveindex plastic that is preferably in the form of a lens and which isthermally compatible with the chip, wire bonds and the connecting leads.

[0004] Careful design of this nature has allowed LEDs to be used inapplications such as automobile rear lights, traffic lights and mostelectronic instrumentation.

[0005] In these applications the light is emitted in a relatively narrowbeam and thus brightness requirements can be satisfied with conventionalLEDs mounted by conventional means.

[0006] In avionic lighting the polar pattern of the light is dictated byauthorities such as the Civil Aviation Authority (UK) or the FederalAviation Authority (US) The polar light pattern is important fornavigation and formation lights because these are intended to indicateto neighbouring aircraft the relative position of the aircraft to eachother to facilitate flying at night. Navigation and formation lights areprovided on wing tips, air intakes and other distinctive parts of theaircraft.

[0007] Night flying is further facilitated by the use of night visiongoggles (NVG) which amplify the low levels of infra red in the nightscene and present the resulting image to the pilot. Advantageouslyaviation external lighting should be virtually free from infra red sothat the goggles of a neighbouring pilot are not blinded which wouldprevent the much lower intensity infrared light from the night scenebeing visible and thus endanger the aircraft. This type of lighting iscalled NVG Friendly.

[0008] This can be achieved with conventional incandescent bulbs by theuse of optical filters (see for example the applicant's own U.S. Pat.No. 6,011,493.

[0009] Because of the nature of light generation in LEDs, the lightoutput has a relatively sharp spectrum and in particular, unlike the“black body” radiation (in accordance with Wien's Law) from a hotincandescent filament, LEDs can be selected which emit very little infrared radiation which makes them particularly suitable for NVG Friendlyaircraft external lighting. Provided the polar light pattern can beachieved and the correct colour and brightness, the reduced maintenanceand improved reliability of LEDs offer significant benefits for theiruse on the outside of aircraft.

[0010] In covert military operations it is required to turn off thevisible lights and to operate with only infra red emitters (ofrelatively low intensity) at the aircraft exterior to enable NVGequipped pilots to “see” neighbouring aircraft. To achieve this, infrared emitting LEDs can be incorporated relatively simply with the visibleLEDs because they use similar power requirements and are physicallysimilar. Again it is important that the polar light pattern of the infrared LEDs is specially designed, the requirement being to signify therelative spatial positions of the aircraft with respect to each otherbut not to observers with NVG on the ground. Typically therefore infrared polar light patterns are such as to minimise infra red emissionsbelow the plane in which the aircraft is flying (so called “below thewater line”). Thus both the polar light patterns of the LEDs (inaccordance with CAA/FAA regulations) and the IR LEDs (for covertoperations) are important and in general terms are different and theyneed to be optimised by careful design of the LED assembly and itsmounting, noting also that the LEDs and IR LEDs generally have differenttransparent lens covers (their primary encapsulation).

[0011] Another problem to address in solid state light design is that ofdissipating the heat from high brightness (and hence high power) solidstate emitters.

[0012] Existing solid state lights have typically been modelled onfilament bulb designs, having tubular bodies (as required for a standardbayonet fitting) with circuitry and a PCB bearing the LEDs mountedwithin die body.

[0013] In accordance with the present invention, there is a lightcomprising a base for mounting the light, a chassis upstanding from thebase, a circuit board mounted upon an outer face of the chassis and atleast one solid state emitter mounted upon the circuit board.

[0014] The arrangement can be constructionally simple while meeting therequirements for heat dissipation and polar light pattern.

[0015] Preferably the chassis comprises a heat sink. The heat sink maybe integrally formed with the chassis. It is particularly preferred thatthe circuit board is mounted on a front face of the chassis and the heatsink projects from the rear of the chassis.

[0016] Still more preferably, the heat sink comprises a set of finsprojecting from the rear of the chassis

[0017] The light preferably comprises a reflector or baffle adjacent thesolid state light emitter(s). This is advantageous in ensuring that therequired polar light pattern is achieved. The reflector or bafflepreferably has a surface which is adjacent the solid state lightemitter(s) and forms an angle, most preferably an acute or right angle,with the portion of the circuit board bearing the emitter(s).

[0018] It is particularly advantageous that the reflector or baffle ismounted on the circuit board. To this end the reflector may be elbowedto provide a reflector/baffle portion and a portion for mounting to thecircuit board.

[0019] The base is preferably provided with means for connection to theelectrical supply.

[0020] In one preferred embodiment, the base is formed as a bayonetfitting. Hence this embodiment can substitute for a bayonet fittingincandescent bulb.

[0021] In a further preferred embodiment, the base has a base surfaceupon which the light rests in use. In such an embodiment the base may beadapted to be bolted in position. This may be by provision of holes forreceipt of a pair of terminal posts, through which the light isconnectable to an electrical supply.

[0022] By allowing the potentially unreliable bayonet fitting(originally designed for easy replacement of the less reliable andvibration sensitive incandescent bulbs) to be dispensed with, thisarrangement allows reliability to be improved.

[0023] It is especially preferred that the circuit board is inclined toa mounting axis of the base. This again can assist in providing arequired polar light pattern.

[0024] The mounting axis is the axis of the bayonet fitting body (inembodiments having this fitting) or is perpendicular to the base surfaceof the light (in embodiments having this feature).

[0025] It is especially preferred that the circuit board is removablymounted upon the chassis. To this end the chassis and circuit board maybe provided with respective contacts arranged to form a circuit forelectrical supply upon mounting of the circuit board to the chassis. Thecontacts may comprise a male contact on one of the circuit board and thechassis and a socket for receiving the male contact on the other of thecircuit board and the chassis.

[0026] The chassis may be provided with means defining a channel forreceipt of an edge of the circuit board. One edge at least of the boardcan thereby be coupled to the chassis in a manner allowing rapidde-coupling.

[0027] Specific embodiments of the present invention will now bedescribed by way of example only, with reference to the accompanyingdrawings, in which:

[0028]FIGS. 1 and 2 are respectively side and front elevations of afirst aircraft light embodying the present invention;

[0029]FIG. 3 is a side elevation corresponding to FIG. 1 but to a largerscale; and

[0030]FIG. 4 is a side elevation of a second aircraft light embodyingthe present invention.

[0031] Both illustrated lights are for mounting inside an aircraftexterior lamp assembly. Both can be used instead of incandescent bulbs.

[0032] The embodiment illustrated in FIGS. 1 to 3 has a base in the formof a mounting block 2. Electrical power supply is via a pair of threadedterminal posts (one of which is seen at 4) bearing nuts 6. The mountingblock 2 is typically bolted to an aircraft borne lamp assembly allowingheat to be conducted away through the lamp assembly to the aircraft.

[0033] Upon the mounting block 2 is a chassis 8 serving to mount aprinted circuit board (PCB) assembly 10. The PCB assembly 10, comprisinga PCB 11, is mounted upon a front face of the chassis which in the FIGS.1 to 3 embodiment is perpendicular to a base surface 12 of the mountingblock. However in alternative embodiments the chassis front face, andhence the PCB assembly, are backwardly inclined (ie. the lower end ofthe PCB is further forward than the upper end) in order to provide arequired polar light pattern.

[0034] Running along a lower edge of the chassis 8 is a retaining clip14 having an upwardly projecting lip 16 forming a channel for receivingthe lower edge of the PCB 11. The PCB's upper region is secured to thechassis by fixing screws 18.

[0035] In this way the PCB assembly 10 is removably mounted upon thechassis.

[0036]FIG. 1 shows the PCB assembly both in place and, at 13, removedfrom the chassis.

[0037] Electrical connections are formed from the two terminal posts 4,along the chassis 8 to respective chassis mounted electrical socketarrangements, one of which is seen at 20. These are positioned toreceive PCB mounted electrical contact pins, one of which is seen at 22,projecting from the PCB's rear face. The pins/sockets can be highreliability items designed for occasional use to military standards. Thepins 22 are connected by PCB tracks to LEDs 24, 26.

[0038] In FIG. 2 it can be seen that the front face of PCB 11 bears anarray of LEDs. In the preset exemplary embodiment these include infrared LEDs 26 as well as visible light LEDs 24. In other embodiments onetype or the other only may be present. The infra red and visible LEDs26, 24 are separately connected allowing switching between the two andcan be connected in series or in parallel or a combination depending onfactors including the voltage available in the aircraft (eg. 28 V.D.C.or 115 V AC at 400 Hz). A suitable arrangement can provide the abilityto simply check whether one LED has failed, where this is in a serieschain making visible to the eye what could otherwise by masked by otherLEDs in the array.

[0039] Regulation of current to the LEDs, and switching between visibleand infra red sources, can be achieved by PCB mounted circuitry. In theillustrated embodiment, block 28 contains a microprocessor for both ofthese functions.

[0040] Secured to the front face of the PCB 11 is a reflector 30. In theillustrated exemplary embodiment this takes the form of an elbowedplate, a first part 32 thereof resting upon and being coupled to the PCB11 and a second, reflector part 34 projecting from the PCB and providingthe required reflective surface 36, which in the illustrated exemplaryembodiment forms an acute angle with the portion of the PCB 11 bearingthe LEDs 24, 26.

[0041] The orientation of the PCB 11, the form of the reflector 30 andthe positioning and properties of the LEDs themselves all contribute inproviding the required polar light pattern.

[0042] A heat sink 38 is provided at the rear of the chassis 8. In theillustrated example the heat sink takes the form of a set of finsintegrally formed with the chassis 8 and projecting rearwardlytherefrom. The PCB 11 has a thermally conductive PC board to provide aroute for heat conduction from the LEDs.

[0043] Whereas FIGS. 1 to 3 concern a light which is bolted into place,FIG. 4 illustrates a light 100 having a base in the form of a bayonetfitting 102 with a lowermost contact 103 and a pair of locating lugs 105which serve also as contacts. The fitting is to be received in astandard light socket allowing the light 100 to be substituted for anexisting incandescent bulb without replacement or removal of the socket.

[0044] The light comprises a PCB assembly 110 similarly formed to thatof the first described embodiment and again having LEDs 124, 126adjacent a reflector 130.

[0045] In the FIG. 4 embodiment the PCB assembly 110 is inclined withrespect to the axis of the bayonet fitting, in order to provide arequired polar light pattern.

[0046] The PCB assembly 110 is mounted upon a chassis 108 comprising anintegrally formed, rearwardly projecting heat sink 138.

[0047] The mounting of the PCB does not utilise a clip as in the FIGS. 1to 3 embodiment.

1. A light comprising a base for mounting the light, a chassisupstanding from the base, a circuit board mounted upon an outer face ofthe chassis and at least one solid state emitter mounted upon thecircuit board.
 2. A light as claimed in claim 1, wherein the chassiscomprises a heat sink.
 3. A light as claimed in claim 2, wherein theheat sink is integrally formed with the chassis.
 4. A light as claimedin claim 2, wherein the circuit board is mounted on a front face of thechassis and the heat sink projects from a rear face of the chassis.
 5. Alight as claimed in claim 4 wherein the heat sink comprises a set ofpins projecting from the rear of the chassis.
 6. A light as claimed inclaim 1, further comprising a baffle adjacent the solid state lightemitter.
 7. A light as claimed in claim 6, wherein the baffle has asurface which is adjacent the solid state light emitter and forms anacute or right angle with the portion of the circuit board bearing theemitter.
 8. A light as claimed in claim 7, wherein the baffle is mountedon the circuit board.
 9. A light as claimed in claim 8 wherein thebaffle is elbowed to provide a baffle portion and a portion for mountingto the circuit board.
 10. A light as claimed in claim 1, provided withmeans for connection to an electrical supply.
 11. A light as claimed inclaim 10, wherein the base comprises a bayonet fitting.
 12. A light asclaimed in claim 10, wherein the base has a base surface upon which thelight rests when mounted and holes for terminal posts through which thelight is connected to an electrical supply.
 13. A light as claimed inclaim 1, wherein the circuit board is inclined to a mounting axis of thebase.
 14. A light as claimed in claim 1, wherein the circuit board isremovably mounted upon the chassis.
 15. A light as claimed in claim 14,wherein the circuit board is provided with contacts arranged to form acircuit for electrical supply upon mounting of the circuit board to thechassis.
 16. A lift as claimed in claim 15, comprising a male contact onone of the circuit board and the chassis and a socket for receiving themale contact on the other of the circuit board and the chassis.
 17. Alight as claimed in claim 1, wherein the chassis is provided with meansdefining a channel for receipt of an edge of the circuit board.
 18. Alight as claimed in claim 1, which is an aircraft light.
 19. A light asclaimed in claim 18, which is NVG friendly.
 20. A light as claimed inclaim 1, wherein both IR and visible solid state emitters are mountedupon the circuit board and are separately connected allowing switchingbetween the two.